Epitaxial formation mechanisms of source and drain regions

ABSTRACT

The embodiments of mechanisms for forming source/drain (S/D) regions of field effect transistors (FETs) descried enable forming an epitaxially grown silicon-containing material without using GeH 4  in an etch gas mixture of an etch process for a cyclic deposition/etch (CDE) process. The etch process is performed at a temperature different form the deposition process to make the etch gas more efficient. As a result, the etch time is reduced and the throughput is increased.

CROSS-REFERENCES TO RELATED APPLICATIONS

The present application is related to U.S. application Ser. No.13/493,626, entitled “EPITAXIAL FORMATION OF SOURCE AND DRAIN REGIONS”filed on Jun. 11, 2012, which is incorporated herein by reference in itsentirety.

TECHNICAL FIELD

The present disclosure relates generally to the field of semiconductordevices and, more particularly, to integrated circuits and fabricationmethods thereof.

BACKGROUND

The semiconductor integrated circuit (IC) industry has experienced rapidgrowth. Technological advances in IC materials and design have producedgenerations of ICs where each generation has smaller and more complexcircuits than the previous generation. However, these advances haveincreased the complexity of processing and manufacturing ICs and, forthese advances to be realized, similar developments in IC processing andmanufacturing are needed.

In the course of IC evolution, functional density (i.e., the number ofinterconnected devices per chip area) has generally increased whilegeometry size (i.e., the smallest component (or line) that can becreated using a fabrication process) has decreased. This scaling downprocess generally provides benefits by increasing production efficiencyand lowering associated costs. Such scaling-down also produces arelatively high power dissipation value, which may be addressed by usinglow power dissipation devices such as complementarymetal-oxide-semiconductor (CMOS) devices.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is best understood from the following detaileddescription when read with the accompanying figures. It is emphasizedthat, in accordance with the standard practice in the industry, variousfeatures are not drawn to scale and are used for illustration purposesonly. In fact, the numbers and dimensions of the various features may bearbitrarily increased or reduced for clarity of discussion.

FIG. 1 is a flowchart illustrating an exemplary method of forming anintegrated circuit.

FIGS. 2A-2E are cross-sectional views of an integrated circuit duringvarious fabrication stages, in accordance with some embodiments.

FIG. 3A is a process sequence of a CDE (cyclic deposition/etch) processin a process chamber, in accordance with some embodiments.

FIG. 3B shows process temperature of a CDE unit cycle, in accordancewith some embodiments.

FIG. 3C shows process pressure of a CDE unit cycle, in accordance withsome embodiments.

FIG. 4 shows a diagram of dissociation rate of HCl as a function oftemperature, in accordance with some embodiments.

FIG. 5A shows a temperature diagram as a function of process time of aCDE unit cycle, in accordance with some embodiments.

FIG. 5B shows a temperature diagram as a function of process time of aCDE unit cycle, in accordance with some embodiments.

DETAILED DESCRIPTION

It is understood that the following descriptions provides many differentembodiments, or examples, for implementing different features of thedisclosure. Specific examples of components and arrangements aredescribed below to simplify the present disclosure. These are, ofcourse, merely examples and are not intended to be limiting. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.Moreover, the formation of a feature on, connected to, and/or coupled toanother feature in the present disclosure that follows may includeembodiments in which the features are formed in direct contact, and mayalso include embodiments in which additional features may be formedinterposing the features, such that the features may not be in directcontact. In addition, spatially relative terms, for example, “lower,”“upper,” “horizontal,” “vertical,” “above,” “below,” “up,” “down,”“top,” “bottom,” etc. as well as derivatives thereof (e.g.,“horizontally,” “downwardly,” “upwardly,” etc.) are used for ease of thepresent disclosure of one feature's relationship to another feature. Thespatially relative terms are intended to cover different orientations ofthe device including the features.

As semiconductor devices, such as metal-oxide-semiconductor field effecttransistors (MOSFETs), are scaled down through various technology nodes,strained source/drain features (e.g., stressor regions) have beenimplemented using epitaxial (epi) semiconductor materials to enhancecarrier mobility and improve device performance. Forming a MOSFET withstressor regions often epitaxially grows silicon (Si) to form raisedsource and drain features for an n-type device, and epitaxially growssilicon germanium (SiGe) to form raised source and drain features for ap-type device. Various techniques directed at shapes, configurations,and materials of these source and drain features have been implementedto further improve transistor device performance. Although existingapproaches have been generally adequate for their intended purposes,they have not been entirely satisfactory in all respects.

The embodiments will be described with respect to specific embodimentsin a specific context, namely a source/drain region for a complementarymetal-oxide semiconductor (CMOS) transistor. The embodiments may also beapplied, however, to other doped regions within a semiconductor device.

Illustrated in FIG. 1 is a flowchart of a method of forming anintegrated circuit, in accordance with some embodiments. FIGS. 2A-2E areschematic cross-sectional views of an integrated circuit during variousfabrication stages, in accordance with some embodiments. The integratedcircuit may include various passive and active microelectronic devices,such as resistors, capacitors, inductors, diodes,metal-oxide-semiconductor field effect transistors (MOSFETs),complementary MOS (CMOS) transistors, bipolar junction transistors(BJTs), laterally diffused MOS (LDMOS) transistors, high power MOStransistors, FinFET transistors, or other types of transistors. It isunderstood that FIGS. 2A-2E have been simplified for a betterunderstanding of the concepts of the present disclosure. Accordingly, itshould be noted that additional processes may be provided before,during, and after the method 100 of FIG. 1, and that some otherprocesses may only be briefly described herein.

Referring now to FIG. 1, the method 100 can include forming a gatestructure over a substrate (block 110). The method 100 can includeremoving portions of the substrate to form recesses adjacent to the gatestructure (block 120). The method 100 can also include forming asilicon-containing material structure in each of the recesses (block130).

Referring now to FIGS. 2A-2E in conjunction with FIG. 1, an integratedcircuit 200 can be fabricated in accordance with the method 100 ofFIG. 1. In FIG. 2A, the integrated circuit 200 can be built on asubstrate 201. Substrate 201 may comprise bulk silicon, doped orundoped, or an active layer of a silicon-on-insulator (SOI) substrate.Generally, an SOI substrate comprises a layer of a semiconductormaterial such as silicon, germanium, silicon germanium, SOI, silicongermanium on insulator (SGOI), or combinations thereof. Other substratesthat may be used include multi-layered substrates, gradient substrates,or hybrid orientation substrates. Substrate 201 may include an epitaxiallayer (epi layer), and may be strained for performance enhancement.

In some embodiments forming n-type transistors, the substrate 201 can bea silicon substrate doped with a p-type dopant, such as boron (resultingin a p-type substrate). A metal gate structure can have a stackstructure including a high dielectric constant gate layer, a diffusionbarrier layer, a metal work function layer, a metallic layer, and/orother suitable layers. A dummy gate structure can have a stack structureincluding a dummy material layer, a hard mask layer, and/or othersuitable layers.

In some embodiments, a gate stack 205 comprising a gate dielectric 207,a gate electrode 209, first spacers 211, and second spacers 212 may beformed over the substrate 201. The gate dielectric layer 207 includes adielectric material, such as silicon oxide, silicon oxynitride, siliconnitride, a high-k dielectric material, or combinations thereof.Exemplary high-k dielectric materials include hafnium oxide (HfO₂),aluminum oxide (Al₂O₃), zirconium oxide (ZrO₂), gallium oxide (Ga₂O₃),titanium oxide (TiO₂), lanthanum oxide (La₂O₃), tantalum oxide (Ta₂O₅),gadolinium oxide (Gd₂O₃), yttrium oxide (Y₂O₃), hafnium dioxide-alumina(HfO₂-Al₂O₃) alloy, hafnium aluminum oxide (HfAlO), hafnium siliconoxide (HfSiO), hafnium silicon oxynitride (HfSiON), hafnium tantalumoxide (HMO), hafnium titanium oxide (HfTiO), hafnium zirconium oxide(HfZrO), titanium aluminum oxide (TiAlO), lanthanum aluminum oxide (suchas LaAlO₃), other high-k dielectric material, or combinations thereof.The gate dielectric layer 207 may include a multilayer structure. Forexample, the gate dielectric layer 207 may include an interfacial layerformed over the substrate 201, and a high-k dielectric layer formed overthe interfacial layer. The interfacial layer may be a silicon oxidelayer formed by a thermal process or ALD process.

The gate electrode layer 209 is disposed over the gate dielectric layer207. The gate electrode layer 209 includes a conductive material, suchas polycrystalline silicon (polysilicon), aluminum (Al), copper (Cu),titanium (Ti), tantalum (Ta), tungsten (W), molybdenum (Mo), platinum(Pt), tantalum nitride (TaN), titanium nitride (TiN), tungsten nitride(WN), titanium aluminum (TiAl), titanium aluminum nitride (TiAlN), TaCN,TaC, TaSiN, other conductive material, or combinations thereof. Theconductive material of the gate electrode layer 209 may be doped orundoped depending on design requirements of field effect transistordevices of integrated circuit 200. In some embodiments, the gateelectrode layer 209 includes a work function layer tuned to have aproper work function for enhanced performance of the field effecttransistor devices of integrated circuit 200. For example, in thedepicted embodiment, where the field effect transistor devices areNFETs, the work function layer includes an n-type work function metal(n-metal), such as Ta, TiAl, TiAlN, TaCN, other n-type work functionmetal, or a combination thereof. Where the field effect transistordevice is a PFET, the work function layer includes a p-type workfunction metal (p-metal), such as TiN, TaN, other p-type work functionmetal, or combination thereof. In furtherance of the present example, aconductive layer, such as an aluminum layer, is formed over the workfunction layer, such that the gate electrode layer 209 includes a workfunction layer disposed over the gate dielectric layer 207 and aconductive layer disposed over the work function layer.

Surrounding the gate stack 205 are the first spacers 211 and the secondspacers 212. The gate stack 205 and the surrounding spacers, such asspacers 211 and 212, form a gate structure 206. The spacer layers maycomprise SiN, oxynitride, SiC, SiON, oxide, and the like. However, asone of ordinary skill in the art will recognize, the first spacers 211and the second spacers 212 as illustrated in FIG. 2A are intended to bemerely illustrative and are not intended to limit the embodiments tothese descriptions. Rather, any suitable number and combination ofspacer layers and shapes may be utilized in order to form spacers forthe gate stack 205, and any suitable combination of spacers mayalternatively be utilized.

In some embodiments of forming an n-type transistor, n-typelightly-doped drains (LDDs) 219 can be formed in the substrate 201.Portions of the n-type LDDs 219 can be formed under the gate structure205. The n-type LDDs 219 can be formed of n-type dopants (impurities).For example, the dopants can comprise phosphorous, arsenic, and/or othergroup V elements. In some embodiments, at least one thermal annealingprocess, e.g., a rapid thermal annealing (RTA) process, can be performedto activate the dopants of the n-type LDDs 219. In some embodiments offorming an n-type transistor, p-type pocket doped regions (not shown)can be formed in the substrate 201. The p-type pocket doped regions canbe formed of p-type dopants (impurities). For example, the dopants cancomprise boron and/or other group III elements.

FIG. 2A illustrates the formation of recesses 210 within the substrate201. The recesses 210 may be formed using, e.g., a wet etch processselective to the material of the substrate 201 and uses the gate stack205, the first spacers 211, and the second spacers 212 as a hard mask inorder to form the recesses 210. For example, an etchant such as carbontetrafluoride (CF₄), HF, tetramethylammonium hydroxide (TMAH), orcombinations of thereof, or the like may be used to perform the wet etchand form the recesses 210. The recesses 210 provide an opening in thesubstrate 201 into which source/drain regions (whose formation isdescribed further below with respect to FIGS. 2B-2E) will subsequentlybe formed.

Recess 210, formed below and between a spacer 212 surrounding gatestructure 205 and a neighboring spacer 212 as shown in FIG. 2A, has awidth W₁ of between about 50 Å and about 500 Å, in accordance with someembodiments. Recesses 210 may additionally undercut the first spacers211 and/or the second spacers 212. Additionally, the wet etch processmay be continued until the recesses 210 have a depth D₁ from a surfaceof the substrate 201. In some embodiments, D₁ is in a range from about50 Å and about 600 Å. However, these dimensions are not intended tolimit the present embodiments, as any suitable dimensions for therecesses 210 may alternatively be utilized.

The recesses 210 may be formed to have either an angular or roundedshape. In an embodiment in which the recesses 210 have an angular shape,the recesses 210 may be formed to have a first angle α₁ along with topof the recesses 210 and a second angle α₂ along the bottom of therecesses 210. In some embodiments, the first angle α₁ is in a range fromabout 90° and about 180°. The second angle α₂ is in a range from about85° and about 170°, in accordance with some embodiments.

Referring to FIGS. 1 and 2B-2E, the method 100 can include forming anepitaxial silicon-containing material structure in each of the recesses(block 130). In some embodiments, the block 130 can include performingan epitaxial deposition/partial etch process and repeating the epitaxialdeposition/partial etch process at least once. Such repeateddeposition/partial etch process is also called a cyclic deposition/etch(CDE) process.

The block 130 may include epitaxially depositing a silicon-containingmaterial (or layer) 215, in recesses 210 as shown in FIGS. 2B-2D, inaccordance with some embodiments. Block 130 also may include depositinga silicon-containing layer 216 over the silicon-containing material 215in recesses 210, as shown in FIG. 2E, in accordance with someembodiments.

The deposition of the silicon-containing material 215 includes in-situdoping the silicon-containing material 215, in accordance with someembodiments. For example, forming an n-type transistor can use an n-typedoping precursor, e.g., phosphine (PH₃) and/or other n-type dopingprecursor. By using the in-situ doping process, the dopant profile ofthe silicon-containing material 215 can be desirably achieved. In someembodiments, the silicon-containing material 215 can be an n-type dopedsilicon layer that is doped with phosphorus (Si:P). In some embodiments,the silicon-containing material 215 can be an n-type doped silicon layerthat is doped with both phosphorus and carbon (Si:CP). Carbon couldimpede the out-diffusion of phosphorus from the silicon-containingmaterial 215. Other types of dopants may also be included. In someembodiments, the phosphorus dopant has a concentration in a range fromabout 0.1% to about 5% (atomic percent). In some embodiments, the carbondopant has a concentration in a range from about 0.1% to about 5%(atomic percent).

In some embodiments, the silicon-containing material 215 can be formedby chemical vapor deposition (CVD), e.g., low pressure CVD (LPCVD),atomic layer CVD (ALCVD), ultrahigh vacuum CVD (UHVCVD), reducedpressure CVD (RPCVD), any suitable CVD; molecular beam epitaxy (MBE)processes; any suitable epitaxial process; or any combinations thereof.In some embodiments, the deposition of the silicon-containing material215 can have a deposition temperature of about 750° C. or less. In otherembodiments, the deposition temperature ranges from about 500° C. toabout 750° C. The pressure of the deposition process can range fromabout 5 Torr to about 500 Torr.

The deposition of the silicon-containing material 215 can use at leastone silicon-containing precursor, such as silane (SiH₄), disilane(Si₂H₆), trisilane (Si₃H₈), Dichlorosilane (SiH₂Cl₂), anothersilicon-containing precursor, and/or any combinations thereof. In someembodiments, the silicon-containing precursor can have a flow rateranging from about 20 standard cubic centimeters per minute (sccm) toabout 500 sccm. In other embodiments forming a p-type transistor, thesilicon-containing material 215 can be made of at least one material,such as silicon, silicon germanium, other semiconductor materials,and/or any combinations thereof.

As mentioned above, the deposition of the silicon-containing material215 includes in-situ doping the silicon-containing material 215, inaccordance with some embodiments. For example, forming an n-typetransistor can use an n-type doping precursor, e.g.,phosphorous-containing gases such as phosphine (PH₃), arsenic-containinggases such as arsine (AsH₃), other n-type dopant-containing gases, or acombination thereof. In some embodiments, the n-type doping precursorcan have a flow rate ranging from about 20 sccm to about 500 sccm. Acarbon-containing gas, such as monomethylsilane (MMS), is also includedto dope the silicon-containing material 215 with carbon, in accordancewith some embodiments. In some embodiments, the carbon-containing gashas a flow rate ranging from about 10 sccm to about 600 sccm.

The silicon-containing material 215 in recesses 210 is epitaxial. Thedeposition process forms a thin epitaxial layer 215 a ofsilicon-containing material in recesses 210 and an amorphoussilicon-containing material 215* on gate electrode 209 and spacers 212,as shown in FIG. 2B in accordance with some embodiments. Referring toFIG. 2C, an etching (or partial etching) process 220 removes theamorphous silicon-containing material 215* and also a portion of thesilicon-containing material 215 a in recesses 210. The remainingsilicon-containing material 215 is formed in each of the recesses 210.In some embodiments, the etching process 220 can use an etching gasincluding at least one of hydrogen chloride (HCl), chlorine (Cl₂),germanium hydride (GeH₄), other suitable etching gases, and/or anycombinations thereof. The flow rate of the etching gas can range fromabout 50 sccm to about 750 sccm, in accordance with some embodiments. Insome embodiments, the pressure of the etching process 220 ranges fromabout 5 Torr to about 500 Torr. In some embodiments, the etching process220 can have an etching temperature of about 590° C. or less. In otherembodiments, the etching temperature can range from about 500° C. toabout 590° C. The process temperatures and pressures for the depositionprocess and etch process to form the silicon-containing material 215 areidentical in some embodiments.

The etching process 220 would remove the amorphous silicon-containingmaterial 215* over non-crystalline surface at a rate higher than theremoval rate of epitaxial silicon-containing material 215. In addition,the etching process would remove a portion of epitaxialsilicon-containing material 215 including the dislocations 241 near thegate corners 240.

The epitaxial deposition/partial etch process is repeated a number oftimes until a desired thickness D₂ is reached, as shown in FIG. 2D inaccordance with some embodiments. As a result, such repeateddeposition/partial etch process is called a cyclic deposition/etch (CDE)process. In some embodiments, D₂ is in a range from about 10 Å and about500 Å. The dotted lines in recesses 210 are used to illustrate themultiple sub-layers formed by the epitaxial CDE process.

As mentioned above, the silicon-containing material 215 can be an n-typedoped silicon layer that is doped with both phosphorus and carbon, inaccordance with some embodiments. Carbon could impede the out-diffusionof phosphorus from the silicon-containing material 215. The phosphorus-and carbon-doped silicon layer can be referred to as a Si:CP layer. Thedopants in the silicon-containing material 215 deposited by CDE havehigher level of activation than implanted dopants. In some embodiments,the dopant activation level is in a range from about 2E20 atoms/cm³ toabout 6E20 atoms/cm³. In contrast, the activation of implanted dopant atS/D is typically at about 1E20 to 2E20 atoms/cm³ level. The higheractivation level makes formation of in-situ doping of epitaxial grownsilicon-containing desirable.

Following the CDE process, a selective epitaxial growth (SEG) processmay be used to deposit additional silicon-containing film to fill theremaining recesses 210. The SEG process has a higher growth rate thanthe CDE process, in accordance with some embodiments. The SEG process isa selective deposition process and the silicon-containing film formed bythis process deposits on epitaxial silicon-containing film, such aslayer 215. SEG processes utilize simultaneous deposition and etch. Insome embodiments, the surface of the silicon-containing layer 216, whichis epitaxial, is leveled with silicon substrate surface 230. In someembodiments, the surface of the silicon-containing layer 216 is abovesilicon substrate surface 230, as shown in FIG. 2E. The thickness D₃ ofthe silicon-containing layer 216 is in a range from about 30 Å to about400 Å, in some embodiments. In some embodiments, the silicon-containinglayer 216 is doped with phosphorus (Si:P).

Layer 215 and layer 216 form the S/D regions 250. In some embodiments,the material and/or method of forming the silicon-containing layer 216can be as same as or similar to those of the silicon-containing material215. In some embodiments, the silicon-containing layer 216 may have adopant concentration different from that of the silicon-containingmaterial 215.

As mentioned above, the process to form the silicon-containing material215 is a CDE process, which involves cyclic deposition and etchprocesses. FIG. 3A shows the process sequence of a CDE process 300 in aprocess chamber, in accordance with some embodiments. The process 300include a deposition operation 301, a post-deposition pump operation302, a partial-etch operation 303, and a post-etch pump operation 304,in accordance with some embodiments. The CDE process occurs in a processchamber. As mentioned above, the deposition operation 201 employs asilicon-containing gas, such as trisilane (Si₃H₈), di-silane (Si₂H₆),etc., as silicon source, and a dopant gas, such as PH₃, is also used toprovide a dopant for the deposited silicon-containing material layer. Insome embodiments, the pressure of the etching process 220 ranges fromabout 5 Torr to about 500 Torr. In some embodiments, the etchingtemperature can range from about 500° C. to about 590° C. In someembodiments, the deposition time is in a range from about 3 seconds toabout 20 seconds. In some embodiments, the amount of thesilicon-containing material 215 deposited in operation 301 is in a rangefrom about 15 Å to about 80 Å during each CDE unit cycle, in accordancewith some embodiments.

After deposition operation 301, a post-deposition pump operation 302 isused to remove the deposition gas from the process chamber. Once thechamber is removed of the deposition gases, the etch operation 303follows. In some embodiments, the etch operation 303 employs HCl gas andGeH₄ gas. A non-reactive carrier gas, such as an inert gas, or N₂, isalso used in the etch gas mixture in accordance with some embodiments.HCl and GeH₄ react with silicon to etch silicon. In some embodiments,GeH₄ acts as an etching catalyst to react with silicon to form SiGe,which is then removed by HCl. The etching temperature and pressure aremaintained at the same levels as the deposition process, in someembodiments. The etch time is in a range from about 40 seconds to about200 seconds, in some embodiments. The amount of the silicon-containingmaterial 215 removed in operation 303 is in a range from about 5 Å andabout 30 Å during each CDE unit cycle, in accordance with someembodiments.

After the etching operation 303, the pump operation 304 follows toremove the etching gases used in operation 303 from the chamber. FIG. 3Bshows process temperature of a CDE unit cycle when the processtemperature is maintained constant (isothermal) T_(CDE) throughout theCDE unit cycle, in accordance with some embodiments. FIG. 3C showsprocess pressure of a CDE unit cycle when the process pressure ismaintained the same (isobaric) P_(CE) during deposition and etchingprocesses, in accordance with some embodiments. Using a CDE process withconstant temperature (isothermal) and the same process pressure(isobaric) during deposition and etch operations has the advantage ofgood process control and chamber matching. In each CDE unit cycle, a netthickness in a range from about 10 Å and about 40 Å is formed in a unitcycle in accordance with some embodiments. After operation 304, theprocess sequence involving operations 301, 302, 303, and 304 repeatagain until the targeted thickness D₂ of silicon-containing material 215is reached.

In the CDE process described above, GeH₄ is used in the etching gasmixture as an etch catalyst. However, the Ge (germanium) in the GeH₄could be incorporated in the silicon-containing material 215unintentionally. The Ge incorporated in the silicon-containing material215 could result in increase in resistivity of silicon-containingmaterial 215. For advanced technology nodes, such as N20 and beyond,such increase of resistivity is unacceptable because of its negativeeffects on Ion (on current) and device performance. In order to removeGeH₄ from the gas mixture, the process condition needs to be adjusted tocompensate for the loss of GeH₄ as the etch catalyst. Without the usageof GeH₄, HCl needs to be dissociated to react with silicon.

FIG. 4 shows a diagram of dissociation rate of HCl in the processchamber as a function of etch temperature, in accordance with someembodiments. The dissociation rate and reactivity of HCl increases withtemperature. HCl dissociates into hydrogen and chlorine at hightemperature. The etch rate of HCl becomes significant at a temperaturenear 600° C. Therefore, the etch temperature should be close to orhigher than 600° C. In some embodiments, the etch temperature of theetch process without GeH₄ is in a range from about 600° C. to about 700°C. By setting the processing temperature of the etch process higher, theetch time can also be shortened to increase process throughput. Inaddition, the etch gas flow rate and pressure can be increased toincrease the etch rate and to shorten etch process time.

FIG. 5A shows a temperature diagram as a function of process time of aCDE unit cycle, in accordance with some embodiments. FIG. 5A shows thatthe deposition occurs at T_(D) and the etch occurs at T_(E). FIG. 5Bshows a pressure diagram as a function of process time of a CDE unitcycle, in accordance with some embodiments. FIG. 5B shows that thedeposition pressure occurs at P_(D) and at P_(E) for the etch.

The deposition process gas mixture has been described above. T_(D) is ina range from about 500° C. to about 590° C., in accordance with someembodiments. T_(E) is in a range from about 600° C. to about 670° C., inaccordance with some embodiments. P_(D) is in a range from about 5 Torrto about 100 Torr, in accordance with some embodiments. P_(E) is in arange from about 50 Torr to about 500 Torr, in accordance with someembodiments. The flow rate of HCl is in a range from about 50 sccm toabout 30 slm (standard liters per minute). A non-reactive carrier gas,such as an inert gas, or N₂, is also used in the etch gas mixture inaccordance with some embodiments. In some embodiments, the carrier gas aflow rate in a range from about 2 slm to about 10 slm.

The deposition process starts at t₁ and occurs for the duration oft_(D). As mentioned above, the deposition time (t_(D)) is in a rangefrom about 3 seconds to about 20 seconds. The etch process starts at t₂and occurs for the duration of t_(E). The next CDE unit cycle starts att₃. With the process change in the etch process, which is without GeH₄,has higher process temperature and pressure than the deposition processand a higher flow rate of HCl compared to the etch process describedabove, the etch time (t_(E)) is also in a range from about 3 seconds toabout 30 seconds, which time and range are shorter than the time andrange of from about 40 seconds to about 200 seconds described above.

Using the processing conditions described above along with FIGS. 5A and5B, the CDE process does not involve GeH₄ as a catalyst, which enablesno Ge incorporation in the silicon containing material 215. Theresistance of silicon containing material 215 without Ge incorporationis reduced consistently across the wafer to a range from about 0.2mohm-cm to about 0.6 mohm-cm, in accordance with some embodiments.Further, by increasing the processing temperature of the etch process inthe CDE unit cycle, the etch process time is greatly reduced.Consequently, the throughputs of the CDE unit cycle and overall CDEprocess are increased.

FIGS. 5A and 5B show that there are temperature ramp-up time, t_(p1),and temperature ramp-down time, t_(p2), to ensure temperatures of theCDE process chamber, substrate holder, and substrate of the CDE processchamber reach the targeted values. To enable fast rise and fall ofprocess temperatures, the process chamber needs to have propertemperature control system. For example, good thermal sensing devicesand sufficient heating and cooling elements are needed. In someembodiments, t_(p1), is in a range from about 5 seconds to about 300seconds. In some embodiments, tp2, is in a range from about 5 seconds toabout 300 seconds.

As noted, the processes of the method 100 described above in conjunctionwith FIGS. 1, 2A-2E, 3A-3C, and 5A-5B are merely exemplary. The method100 can include different steps according to different process flows.For example, the gate structure 205 can be formed by a gate-firstprocess or a gate-last process. In some embodiments using a gate-lastprocess, the method 100 can include a gate replacing process. The gatestructure 205 can be a dummy gate structure. The dummy gate structure205 can each include a dummy gate material and a hard mask materialformed thereover. The dummy gate material can be made of at least onematerial such as polysilicon, amorphous silicon, silicon oxide, siliconnitride, a material having an etching rate that is substantiallydifferent from the spacers (shown in FIG. 2A).

For the gate-last process, the hard mask materials and the dummy gatematerials can be removed, for example, by a wet etch process, a dry etchprocess, or any combinations thereof. After removing the dummy gatematerials, the method 100 can include forming gate electrode materialwithin openings in which the dummy gate materials are disposed. In someembodiments, the gate electrode material can be a stack structureincluding a diffusion barrier layer, a metallic work function layer, ametallic conductive layer, and/or other suitable material layers.

The embodiments of mechanisms for forming source/drain (S/D) regions offield effect transistors (FETs) descried enable forming an epitaxiallygrown silicon-containing material without using GeH₄ in an etch gasmixture of an etch process for a cyclic deposition/etch (CDE) process.The etch process is performed at a temperature different from thedeposition process to make the etch gas more efficient. As a result, theetch time is reduced and the throughput is increased.

In some embodiments, a method of forming an integrated circuit isprovided. The method includes forming a plurality of gate structuresover a substrate, and removing portions of the substrate to formrecesses adjacent to the plurality of gate structures. The method alsoincludes depositing a first epitaxial silicon-containing layer in therecesses, and depositing the first epitaxial silicon-containing layeruses a cyclic deposition etching (CDE) process. The CDE process has aCDE unit cycle, and the CDE unit cycle has a deposition process and anetch process. The CDE unit cycle uses an etch temperature of the etchprocess is different from a deposition temperature of the depositionprocess in the CDE unit cycle. The method further includes depositing asecond epitaxial silicon-containing layer over the first epitaxialsilicon-containing layer to form source and drain regions next to theplurality of gate structures.

In some other embodiments, a method of forming an integrated circuit isprovided. The method includes forming a plurality of gate structuresover a substrate, and removing portions of the substrate to formrecesses adjacent to the plurality of gate structures. The method alsoincludes depositing a first epitaxial silicon-containing layer in therecesses, and depositing the first epitaxial silicon-containing layeruses a cyclic deposition etching (CDE) process. The CDE process has aCDE unit cycle, and the CDE unit cycle has a deposition process and anetch process. The CDE unit cycle uses an etch temperature of the etchprocess is higher from a deposition temperature of the depositionprocess in the CDE unit cycle. The method further includes depositing asecond epitaxial silicon-containing layer over the first epitaxialsilicon-containing layer to form source and drain regions next to theplurality of gate structures.

In yet some other embodiments, an integrated circuit is provided. Theintegrated circuit includes a gate structure disposed over a substrate,and a silicon-containing material structure formed in and over a recessadjacent to the gate structure. The silicon-containing materialstructure includes a first epitaxial layer and a second epitaxial layer.The first epitaxial layer has a resistance in a range from about 0.2mohm-cm to about 0.6 mohm-cm.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method of forming an integrated circuit, themethod comprising: forming a plurality of gate structures over asubstrate; removing portions of the substrate to form respectiverecesses adjacent to the plurality of gate structures; depositing afirst epitaxial silicon-containing layer in the recesses, whereindepositing the first epitaxial silicon-containing layer uses a cyclicdeposition etching (CDE) process, wherein the CDE process has a CDE unitcycle, wherein the CDE unit cycle has a deposition process and an etchprocess, wherein the CDE unit cycle uses an etch temperature of the etchprocess that is different from a deposition temperature of thedeposition process in the CDE unit cycle; and wherein the CDE processincludes a deposition, a pump after deposition, an etch, and a pumpafter etch in each deposition and etch cycle, and wherein the CDEprocess is performed in the same process chamber; and depositing asecond epitaxial silicon-containing layer over the first epitaxialsilicon-containing layer to form respective source and drain regionsnext to the plurality of gate structures.
 2. The method of claim 1,wherein the etch temperature is higher than the deposition temperaturein the CDE unit cycle.
 3. The method of claim 2, wherein the etchtemperature used enables no usage of GeH₄ in an etch gas mixture of theetch process.
 4. The method of claim 1, wherein the etch process of theCDE unit cycle uses GeH₄.
 5. The method of claim 1, wherein the etchtemperature is in a range from about 600° C. to about 700° C.
 6. Themethod of claim 1, wherein the deposition temperature is in a range fromabout 500 ° C. to about 590° C.
 7. The method of claim 1, wherein apressure of the etch process is in a range from about 50 Torr to about500 Torr.
 8. The method of claim 1, wherein a pressure of the depositionprocess is in a range from about 5 Torr to about 100 Torr.
 9. The methodof claim 1, wherein a flow rate of HCl gas used in the etch process isin a range from about 50 sccm to about 30 slm.
 10. The method of claim1, wherein an etch time for the CDE unit cycle is in a range from about3 second to about 30 second.
 11. The method of claim 1, wherein etchgases of the etching process of the CDE unit cycle include HCl.
 12. Themethod of claim 1, wherein the recesses have a depth in a range fromabout 200 Å to about 400 Å.
 13. The method of claim 1, wherein athickness of the first epitaxial silicon-containing layer is in a rangefrom about 70 Å to about 300 Å, wherein the first epitaxialsilicon-containing layer is doped with phosphorus and carbon, whereinthe concentration of the phosphorus is in a range from about 0.3% toabout 2%.
 14. The method of claim 1, wherein a resistivity of the firstepitaxial silicon-containing layer is in a range from about 0.2 mohm-cmto about 0.6 mohm-cm.
 15. A method of forming an integrated circuit, themethod comprising: forming a plurality of gate structures over asubstrate; removing portions of the substrate to form recesses adjacentto the plurality of gate structures; depositing a first epitaxialsilicon-containing layer in the recesses, wherein depositing the firstepitaxial silicon-containing layer uses a cyclic deposition etching(CDE) process, wherein the CDE process has a CDE unit cycle, wherein theCDE unit cycle has a deposition process and an etch process, wherein theCDE unit cycle uses an etch temperature of the etch process that ishigher than a deposition temperature of the deposition process in theCDE unit cycle; and wherein the CDE process includes a deposition, apump after deposition, an etch, and a pump after etch in each depositionand etch cycle, and wherein the CDE process is performed in the sameprocess chamber; and depositing a second epitaxial silicon-containinglayer over the first epitaxial silicon-containing layer to form sourceand drain regions next to the plurality of gate structures.
 16. A methodof forming an integrated circuit, the method comprising: forming a ofgate structures over a substrate, the gate structure including a gatedielectric and a gate electrode formed thereon; forming gate spacers onsidewalls of the gate structure; using the gate structure and gatespacers as a mask, etching portions of the substrate to form respectiverecesses aligned with edges of the gate spacers; depositing a firstepitaxial silicon-containing layer in the recesses, wherein depositingthe first epitaxial silicon-containing layer uses a cyclic depositionetching (CDE) process, wherein the CDE process has a CDE unit cycle,wherein the CDE unit cycle has a deposition process and an etch process,wherein the CDE unit cycle uses an etch temperature of the etch processthat is different from a deposition temperature of the depositionprocess in the CDE unit cycle; and wherein the CDE process includes adeposition, a pump after deposition, an etch, and a pump after etch ineach deposition and etch cycle, and wherein the CDE process is performedin the same process chamber; and depositing a second epitaxialsilicon-containing layer over the first epitaxial silicon-containinglayer to form respective source and drain regions next to the pluralityof gate structures.
 17. The method of claim 16, wherein the etchtemperature is in a range from about 600° C. to about 700° C. and thedeposition temperature is in a range from about 500° C. to about 590° C.18. The method of claim 16, wherein a pressure of the etch process is ina range from about 50 Torr to about 500 Torr and a pressure of thedeposition process is in a range from about 5 Torr to about 100 Torr.19. The method of claim 16, wherein etching portions of the substrateincludes undercutting the respective spacers.
 20. The method of claim16, wherein the etching process uses an etching gas including a gasselected from the group consisting of hydrogen chloride (HCl), chlorine(Cl₂), germanium hydride (GeH₄), and combinations thereof.